A number of applications that involve the thermal processing of substrates such as semiconductor wafers and other materials involve the process steps of rapidly heating and cooling a substrate. One example of such processing is rapid thermal processing (RTP), which is used for a number of fabrication processes.
Rapid thermal processing (RTP) systems are employed in semiconductor chip fabrication to create, chemically alter or etch surface structures on semiconductor wafers. One such RTP system, as described in U.S. Pat. No. 5,155,336, which is assigned to the assignee of the subject application and which is incorporated herein by reference, includes a semiconductor processing chamber and a heat source assembly or lamphead located on the semiconductor processing chamber. A number of infrared lamps are located in the lamphead. During processing, infrared radiation from the lamps radiate through an upper window, light passageways and a lower window onto a rotating semiconductor substrate in the processing chamber. In this manner, the wafer is heated to a required processing temperature. During semiconductor processing operations, the lamps operate at extremely high temperatures. Not all of the electrical energy delivered to an RTP chamber lamphead ends up actually heating the wafer. Some of the radiant energy is absorbed by chamber components, especially the reflective components in the radiation field.
A heating lamp may be contained in an assembly having a reflector sleeve, for example, as described in U.S. Pat. No. 6,072,160, which is assigned to the assignee of the present application and which is incorporated herein by reference in its entirety. A heating lamp may also be contained in a monolithic lamphead having a plurality of lamp receptacles as described in U.S. Pat. No. 6,805,466, which is assigned to the assignee of the subject application, and which is incorporated herein by reference in its entirety.
In general, reflector sleeves or a monolithic lamphead have a reflective layer which contains a layer or coating made of gold. However, gold does not have optimal reflective properties compared to silver. In addition, gold is substantially more expensive than silver. However, silver has not been used as a reflective material in lamps due to a severe problem of the silver tarnishing, which renders silver useless as a reflective material because the surface of the silver turns black, destroying the ability of it to reflect. Accordingly, novel and improved reflectors, reflector materials and methods for improved reflection of radiation are required for RTP and semiconductor processing applications.